Facing a storm of global criticism over an ethnic slaughter in her home country, the Nobel laureate who is Myanmar’s most prominent political leader has canceled her planned visit to the United Nations General Assembly.

The cancellation by the leader, Daw Aung San Suu Kyi, was announced by her office on Wednesday, less than a week before the annual gathering in New York of leaders representing the 193-member General Assembly, the largest forum for diplomacy.

Her decision to abandon the visit came amid an uproar over deadly attacks by security forces on Rohingya Muslims in Myanmar, which is predominantly Buddhist.

In recent weeks, hundreds have been killed, including children. Nearly 400,000 have fled for their lives into neighboring Bangladesh, according to officials and news reports from the region.

A chorus of international leaders and human rights groups have denounced the attacks as ethnic cleansing — some have called it genocide — and have castigated Ms. Aung San Suu Kyi over what they described as her indifference.

“She’s keeping silent, and that silence is essentially a green light for the military,” said Louis Charbonneau, the United Nations director at Human Rights Watch.

While Ms. Aung San Suu Kyi’s views on the Rohingya killings are not clear, she caused an uproar last week, partly attributing alarm about the crisis to a “huge iceberg of misinformation” while discussing it with President Recep Tayyip Erdogan of Turkey.

“Everything she has said doesn’t inspire confidence that she’s on the right side of this issue,” Mr. Charbonneau said.

Some critics have called for Ms. Aung San Suu Kyi to be stripped of her Nobel Peace Prize, which she won in 1991 for standing up to Myanmar’s military junta in a campaign for democracy.

There had been widespread expectation that she would speak about the Rohingya killings at the General Assembly. But a spokesman for her office, Zaw Htay, told reporters in Myanmar on Wednesday that she had canceled her trip because of the crisis.

“She is concentrating on establishing stability,” the spokesman said in remarks quoted by news agencies.

News of the canceled visit came as pressure has intensified at the United Nations for action to halt the killings.

The United Nations secretary general, António Guterres, told reporters on Wednesday that the Rohingya situation was “catastrophic.”

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“By far the worst thing that I've ever seen.” The New York Times reporter Hannah Beech describes a huge exodus of civilians into Bangladesh after a new military offensive against Rohingya Muslims in Myanmar.CreditCreditAdam Dean for The New York Times

“When one-third of the Rohingya population has to flee the country, can you find a better word to describe it?” Mr. Guterres responded.

Mr. Guterres was addressing reporters in an hourlong news conference ahead of speeches next week by presidents and prime ministers at the General Assembly.

“This is a dramatic tragedy,” he said. “People are dying and suffering at horrible numbers and we need to stop it.”

In recent days, the exodus of Rohingya fleeing the violence into Bangladesh has tripled. Mr. Guterres said he had spoken “several times” with Ms. Aung San Suu Kyi, though not since her office confirmed that she would not attend the General Assembly.

She attended last year for the first time, and she asserted that her government was “standing firm against the forces of prejudice and intolerance” in Rakhine State, where most of the Rohingya population lives.

Mr. Guterres took the unusual step last week of having asked the Security Council to help end the military strikes against the Rohingya. The 15-member body, empowered to impose sanctions and other measures against the government of Myanmar, met privately as he spoke.

Members of the Security Council emerged later Wednesday afternoon to express “concern about reports of excessive violence during security operations” in Rakhine and called for “immediate steps to end the violence.”

It was part of what, in the diplomatic language at the United Nations, is known as press elements, the weakest form of pronouncement that can be made by the Security Council.

The British ambassador, Matthew Rycroft, called it “an important first step.”

Britain’s foreign secretary, Boris Johnson, is to preside over a meeting on Myanmar with other foreign ministers on the sidelines of the General Assembly next week, Mr. Rycroft said.

Ms. Aung San Suu Kyi, a 72-year-old widow, endured many years of house arrest for her defiance of Myanmar’s generals and had long been considered a heroine of modern times.

She resumed her national political prominence after her release in 2010. The country’s majority party introduced a bill in Parliament last year and created a new post for her as state counselor, which some analysts have compared to the role of a prime minister.

Ms. Aung San Suu Kyi is prohibited under the country’s Constitution from becoming president, because her children are British citizens, as was her husband. But in her role as state counselor, as well as leader of the majority party in Parliament, she is the most powerful person in the government.

The anger and despondency over her failure to stop the Rohingya persecution has spread to her fellow Nobel laureates.

In an open letter to Ms. Aung San Suu Kyi published last week, Archbishop Desmond Tutu of South Africa said, “My dear sister: If the political price of your ascension to the highest office in Myanmar is your silence, the price is surely too steep.”

Tess Felder contributed reporting.

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